1. Field of the Invention
The present invention relates to a method for enhancing the controlling function of a mass flow controller (MFC) controlling device and for automation thereof and further relates to a corresponding system.
2. Description of Related Art
A conventional MFC controlling device mostly uses a PI or PID controller. The controlling device works by manual adjusting with parameters that are set empirically, based on response signals of a measured gas flow which are combined.
FIG. 2 is a flow chart of a manually adjusted PI controller of a conventional MFC controlling device. At a given pressure 1 and a given flow rate 2, manually adjusted control parameters 3 are applied to the MFC controlling device. Response characteristics 4 of the MFC are measured, like rise time, settling time and overshoot. Only after passing a judgment whether all parameters match a standard 5 in the positive, further conditions of the pressure and gas flow are determined, and equal manually adjusted control parameters 3 are applied. These steps are repeated until a judgment whether pressure values and gas flow rates have been completely settled 6 is done in the positive, which finishes the process. This conventional process has an inner and an outer loop, with parameters that often contradict each other and are difficult to harmonize. Therefore the conventional method of manual control parameters is difficult to perform, inefficient and slow, leaving the quality of produced articles hard to control. To summarize, a conventional MFC controlling device has the following three grave disadvantages:
1. When the conventional method of manual control parameters is applied to an MFC controlling device, manual measurements have to be performed repeatedly and adjustments need to be done in a complicated process. Therefore, appropriate adjusting of control parameters in a method using a conventional MFC controlling device requires a lot of time and effort. Simply said, a method using a conventional MFC controlling device is inefficient and not economical.
2. Generation of MFC valve exhaust: Basically, an MFC controlling device has to be adapted to pressures of 8-50 psi for regular operation. However, in practice, an MFC valve has characteristics which naturally vary with changes of working gas pressure and flow. Therefore, only after having passed through all kinds of pressure and flow values and through several measurement cycles, control parameters will arrive at suitable values. Occasionally, manual empirically based parameters take a lot of time and still do not find suitable values. Under economic constraints, often discarding the MFC state has to be considered, which is wasteful.
3. Poor capacity of the MFC controlling device: Since the MFC valve has changing characteristics under varying gas pressure and flow, using a manually control led MFC controlling device even at great effort often implies only one or two sets of PID control parameters. Therefore, the response characteristics of a manually control led MFC controlling device in practice do not warrant generating and maintaining good controlling behavior under various working flows and pressures. For these reasons, the control characteristics of conventional MFC controlling devices need to be improved.
It is an object of the present invention to provide a mass flow controller controlling device automation method and related system which combines an identification technique and fuzzy theory, so as to achieve an enhanced controlling function of the mass flow controller as well as an increased economical effect thereof.
Another object of the present invention is to provide a process for generating parameters in a mass flow controller controlling device which needs no manual adjusting, working automatically, so as to increase production rates and reduce costs.
By achieving the above objects, the present invention completely resolves the three disadvantages of conventional MFC controlling devices, offering as a main advantage a good economical effect of the MFC valve.
The present invention can be more fully understood by reference to the following description and accompanying drawings.